BuTripMode is set 1 out of 4. The current setting should be chosen in accordance tothe setting of the sensitive earth-fault protection. The setting can be given withinthe range 2 – 200 % of IBase.t1: Time delay of the re-trip. The setting can be given within the range 0 – 60s insteps of 0.001 s. Typical setting is 0 – 50ms.t2: Time delay of the back-up trip. The choice of this setting is made as short aspossible at the same time as unwanted operation must be avoided. Typical setting is90 – 200ms (also dependent of re-trip timer).The minimum time delay for the re-trip can be estimated as:_2 1³ + + +cbopen BFP reset margint t t t tEQUATION1430 V1 EN-US (Equation 34)where:tcbopen is the maximum opening time for the circuit breakertBFP_reset is the maximum time for breaker failure protection to detect correct breaker function (thecurrent criteria reset)tmargin is a safety marginIt is often required that the total fault clearance time shall be less than a givencritical time. This time is often dependent of the ability to maintain transientstability in case of a fault close to a power plant.1MRK 504 169-UEN A Section 7Current protectionTransformer protection RET650 2.2 IEC 139Application manual
